Shoryamishra61 opened a new pull request, #25475:
URL: https://github.com/apache/datafusion/pull/25475
## Which issue does this PR close?
- Closes #25462
## Rationale for this change
When converting DataFusion logical expressions back to SQL AST in
`datafusion-sql`, both `Expr::WindowFunction` and `Expr::AggregateFunction`
previously dropped the `null_treatment` field stored in `WindowFunctionParams`
and `AggregateFunctionParams` and hardcoded `null_treatment: None` on the
generated `sqlparser::ast::Function`.
As a result, expressions using `IGNORE NULLS` or `RESPECT NULLS` (such as
`FIRST_VALUE(v IGNORE NULLS) OVER (...)` or aggregate `FIRST_VALUE(v IGNORE
NULLS)`) lost their explicit NULL treatment clause during unparsing, altering
query semantics upon re-execution.
## What changes are included in this PR?
- Extracted `null_treatment` from `WindowFunctionParams` in
`Expr::WindowFunction` and forwarded it to `ast::Function.null_treatment`.
- Extracted `null_treatment` from `AggregateFunctionParams` in
`Expr::AggregateFunction` and forwarded it to `ast::Function.null_treatment`.
- Added helper function `null_treatment_to_sql` mapping
`datafusion_expr::expr::NullTreatment` to `sqlparser::ast::NullTreatment`.
- Added unit tests covering `IGNORE NULLS`, `RESPECT NULLS`, and `None`
(control) for both window and aggregate functions.
## What is the testing strategy for this PR?
- Added `test_unparse_null_treatment_window_and_aggregate` in
`datafusion/sql/src/unparser/expr.rs` covering:
- Window functions with `IGNORE NULLS`
- Window functions with `RESPECT NULLS`
- Window functions without explicit NULL treatment (control case ensuring
no clause is emitted)
- Aggregate functions with `IGNORE NULLS`
- Aggregate functions with `RESPECT NULLS`
- Aggregate functions without explicit NULL treatment (control case)
- Verified test fails on pre-fix code and passes with the fix.
- Ran all unparser unit tests: `cargo test -p datafusion-sql --lib unparser`
(38 passed, 0 failed).
- Verified lints and formatting: `cargo fmt --all -- --check` and `cargo
clippy -p datafusion-sql --all-targets --all-features -- -D warnings`.
## Are there any user-facing changes?
Bug fix: SQL unparsing now preserves explicit `IGNORE NULLS` and `RESPECT
NULLS` clauses on window and aggregate functions rather than omitting them.
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